The overall theme of this proposal is to gain insight into the molecular pathways that control cardiac gene expression and the hypertrophic growth of the myocardium. The focus of this proposal is to analyze one family of transcriptional regulators to assess their potential role in directing these processes. Specifically, the functions of the zinc- finger transcription factors GATA4, 5, and 6 will be analyzed to determine their potential contribution to the establishment of the cardiac gene program and in controlling altered gene expression associated with the hypertrophic response. Our unifying hypothesis states that GATA4, 5, and 6 are required for the establishment and maintenance of the cardiac differentiation-specific gene program. The three cardiac-expressed GATA DNA binding factors are known regulators of differentiation-specific genes such as the alpha-myosin heavy chain, cardiac troponin-C, atrial natriuretic factor, and brain natriuretic peptide. Recent investigations have also directly implicated GATA4 as a transcriptional regulator of the hypertrophic response itself. However, the molecular mechanisms whereby GATA4, 5, and 6 function to control the cardiac differentiation-specific gene program and the hypertrophic growth of the myocardium are not well understood. In fact, very little appreciation exists within the field as to the necessary functions of the three cardiac-expressed GATA factors in directing cardiac transcriptional events. Towards this end, two approaches are outlined within this proposal. 1) A genetic evaluation in the mouse will be undertaken to determine the necessary and sufficient functions mediated by GATA4, 5, and 6 in establishing the cardiac gene-specific program. 2) A biochemical evaluation in cultured primary cardiomyocytes will also be undertaken to elucidate the transcriptional regulatory networks whereby GATA4, 5, and 6 act to regulate cardiac-specific gene expression and the hypertrophic response. An understanding of the regulatory networks that act to control cardiac differentiation-specific gene expression at steady state and in response to stress will be instrumental in dissecting the altered transcriptional networks that act during various forms of heart disease.